Note from Markus Fleschutz: 
    
    * data downloaded on 2021-06-10
    * from https://www.smard.de/en/downloadcenter/download-market-data#!?downloadAttributes=%7B%22selectedCategory%22:3,%22selectedSubCategory%22:8,%22selectedRegion%22:%22DE%22,%22from%22:1420066800000,%22to%22:1451602799999,%22selectedFileType%22:%22CSV%22%7D
    * License: CC BY 4.0